The present invention relates generally to the bonding of silicone rubber films to polyester films and particularly to the bonding of silicone rubber films to polyethylene terephthalate polyester films which are exposed in use to chemical challenge.
Silicone rubber-polyethylene terephthalate polyester film bonds have been previously prepared by a bonding process known as "priming". This "priming" process was capable of developing strong adhesive bonds between room temperature vulcanizing (RTV) silicone rubber and polyethylene terephthalate (PET) film, but the resultant bonds lacked long term stability in an presence of water and alcohol. This lack of stability is thought to be due to hydrolysis of the relatively weak mechanical bond formed by and characteristic of this process.
The "priming" process involved first cleaning the polyester film using sequentially, a detergent solution, a de-ionized water rinse and a rinse with solvents. Then, a proprietary primer based upon a silicone resin suspended in an ethyl acetate solution is applied to the polyester film. Thereafter, the polyester film is dried to remove all volatile materials. Lastly, the RTV silicone resin is mixed with its catalyst and applied to the polyester film.
These silicone rubber-polyester bonded composites are formed in a variety of manufactured items, among them certain medical devices such as ultra-sound transducers. In the instance of the transducer, the silicone rubber-polyester bonds routinely come into contact with one or both of water or alcohol, and it has become necessary to find a bonding process for the preparation of a RTV silicone rubber-PET film bond which would possess reduced or eliminated susceptibility to these chemical agents. It is therefore to the solution of the aforenoted problem that the present invention is directed.